Computer: Definition and History

Lin ZhongELEC101, Rice University

What makes a computer?

What did you do to the NXT, indeed?

lab1.nxc

lab1.rxe

Compiler

Program as understood by NXT

What does it take NXT to achieve it?

• Interface to receive your instructions• Store your instructions• Execute your instructions– Sense– Calculate– Actuate

Computer: definition

• Programmable machine that receives input, stores and automatically manipulates data, and provides output in a useful format– Wikipedia

Elementary functions of computer

• Communication– Input– Output

• Storage

• Processing (calculation/manipulation)

Computer: definition

• Programmable machine that receives input, stores and automatically manipulates data, and provides output in a useful format– Wikipedia

Key features of computer

• Programmable– Take new instructions

• Automatic– Involving human as little as possible

• Useful– Serve a human purpose

Questions to answer

• Why does NXT accept instructions in 0s and 1s?

• How does NXT store instructions?

• How does NXT interpret the instructions?

Key concepts

• State, data, and information• Computing– How to store, change, and communicate

information• Analog signal vs. digital signal

• State in various incarnations

13

State vs. Data vs. Information

• State– The physical property of a physical entity

• Data– State measurement properly represented

• Information– “Meanings” carried by signal/data– Can be measured (entropy)

14

Objective

Subjective

Computing

• Human function– Process information– Store information– Communication information

• Physical realization– Modification (Processing) of a state– Storage of a state– Communication of a state

15

The world is analog

• Analog states– Continuous in both time and amplitude– Temperature as example

• Practical challenges to analog state– For example, tell a friend about the classroom

temperature

16

Analog to digital: Quantization

17

Amplitude

TimeDiscrete value, continuous time

Why could the information loss be fine?

Analog to digital: Sampling

18

Amplitude

TimeDiscrete time, continuous value

Why could the information loss be fine?

Digital signal

19

Amplitude

Time

Discrete value, discrete time

20

Era of mechanical states

Chinese abacus

Punched card based “computers”

• Two states: presence or absence of hole

Jacquard loom (1801)

• Punched cards control positions of hooks for weaving

• More: fairground organ, player piano,….,

Mechanical computer • Charles Babbage (1791-1871)

– Difference Engine– Analytical Engine

• First programmable computer• First programmer (Ada Lovelace)

23

WWW

Mechanical calculator (1900s to 1960s)

241964

1958

251966

Problems with mechanical states

• To change a state

• To store a state

• To communicate a state

26